A description of the basic interventional procedure which can be performed with an imaging system for ‘Percutanerous Transluminal Coronary Angioplasty’ (PTCA), to treat cardiac stenoses, can be found in “Algorithmic Solutions for Live Device-to-Vessel Match”. J. Bredno, B. Martin-Leung & K. Eck. In Proceedings of SPIE—Volume 5370—Medical Imaging 2004: Image Processing, J. Michael Fitzpatrick, Milan Sonka, Editors, May 2004, pp. 1486-1497.
There is written: ‘After a catheter is inserted into the vascular system at an access site, it is advanced along large vessels to the vascular structure that requires treatment. Contrast agent is injected via the catheter and cathlab x-ray equipment records an angiographic sequence that shows the vessels when filled with contrast agent. The diagnostic angiogram acquisitions can be repeated with varying imager geometries. Diagnosis and intervention planning are based on such diagnostic angiograms ( . . . ). During intervention, a flexible, partially or fully radio-opaque guidewire is advanced to the affected vascular structures (e.g. stenoses in coronaries, neurovascular aneurisms, or arterio-venous malformations). Fluoroscopic low-dose x-ray surveillance visualizes the guidewire ( . . . ) and allows for the hand-eye-coordination of the interventionalist while advancing the guidewire. When positioned, the guidewire serves as rail to deliver interventional devices (e.g. balloons for dilation and stent delivery, detachable coils for aneurysm clotting). The delivery and deployment of the interventional devices is also fluoroscopy-controlled.’
Now, one of the most delicate phases during PTCA is the passing of the guide-wire tip through the targeted lesion (stenosis). The vessel walls at this location are usually uneven, and by definition, the conduct is narrowed. It follows that stenosis passing is one of the most time consuming (and therefore dose generating) parts of the intervention.
Another delicate phase consists in positioning the balloon or stent markers with respect to the target lesion. The accuracy of this positioning is very important because it determines where the balloon and/or stent are to be deployed.
One of the reasons why the stenosis passing phase is difficult comes from the fact that it is achieved almost blindly and on a moving target. Most of the time, the cardiologist only sees the wire tip while trying to figure out what the stenosis looks like and what is the exact location of the tip within that stenosis. In this process, the cardiologist often injects a small shot of contrast agent to help figuring out where the tip is with respect to the stenosis, and then proceeds with the intervention. Likewise, when positioning the balloon/stent markers with respect to the stenosis, the cardiologist injects a small amount of contrast agent to determine how the markers should be moved to reach the optimal localisation.
In both cases (stenosis passing and marker positioning) contrast injection helps, but it still involves a difficult process because of a variety of factors including:
the presence of many motions (cardiac, respiratory, contrast agent flow, device),
the fact that due to motion, zooming is limited,
the poor contrast in the images due to the fluoroscopy conditions.
Now, in order to improve the situation, one can use a technique referred to as device boosting (see for instance “Registration and Integration for Fluoroscopy Device Enhancement”. James C. Ross, David Langan, RaviManjeshwar, John Kaufhold, Joseph Manak, and David Wilson. Miccai 2005.), where one compensates for the device motion while enhancing the device visibility with temporal integration.
For device boosting, a viewing system performing an image processing method can be used. The viewing system comprises means for acquiring a sequence of images, and for processing and displaying said images in real time. The system comprises initialization means applied to the original images for extracting and localizing an object of interest, which may be moving with respect to the referential of the image, the background being moving both with respect to said referential and with respect to the object. The initialization means then comprise registration means for registering the object of interest with respect to the referential of the image. This system further comprises processing means for automatically enhancing the object of interest, for minimizing the noise and for blurring or fading the background of the images. Said processing means include at least a means for carrying out a temporal integration technique performed on at least two images where the object of interest has been registered with respect to the referential of the images. Since after registration of the object, the background still moves with respect to the referential of the images, this temporal integration technique provides an enhancement of the object of interest, while minimizing the noise and blurring and fading the background.
However, if the device moves with respect to the surrounding anatomy (which is usually the case for the applications presented above), then device-based registration and integration is bound to degrade the anatomy visibility (becoming blurred), and thus to degrade the device localisation with respect to this anatomy.